text: Using Fouriers law of heat conduction, the general equation for temperature change in a medium through conduction is:where  is the mediums density,  is the heat capacity at constant pressure, and  is the thermal conductivity.  If the thermal conductivity depends on temperature according to the power law:Then the heat transfer equation may be written as the porous medium equation:with  and .  The thermal conductivity of high-temperature plasmas seems to follow a power law.